A typical bone plate such as described in WO 2004/089233 of Thielke, US 2006/0229619 of Orbay, US 2006/0235404, or US 2007/0055253 all of Orbay, extends along an axis and has an outer end that is fan-shaped and formed with an array of holes so that it can be solidly screwed to the epiphysis or bone head to one side of the fracture or other injury that is to be reduced so the bone can grow back together. Extending from this fan-shaped outer end is a flat narrow bar formed with another array of holes allowing it to be screwed to the bone's shaft or diaphysis. The most common use of such a bone plate is in setting or reducing a distal fracture of the radius, but it can of course also be used for any type of fracture on a distal portion of a long bone.
Such a bone plate is used to hold the broken bone together at the fracture so that by arthrodesis the bone will knit back together. Once the fracture has mended the plate may be removed. Such a plate allows for a faster reduction of the break by biasing it together, to prevent later phenomena such as arthrosis.
In the case of distal fractures of the radius, plates allowing for a positioning in length by means of an oblong hole are already known. Such plates, which return the distal fragment to the correct spacing and fix it by adjusting the plate in length before it is locked in the diaphysis, do not however enable any lateral adjustment. The bone plate of US 2007/0233114 of Bouman has transverse and longitudinal slots allowing some longitudinal and transverse relative shifting of parts, but in a structure intended for use on a bone shaft.
Because of the exigencies of surgery, in some cases it is necessary to first fix the distal fragments of the radius on the plate before the fracture is reduced on the diaphysis.
One can, however, never be sure of the orientation of the plate, which therefore is not always on the axis of the radius. In this case the elongated diaphysial or inner portion of the broken bone might be offset transversely and thus make the patient uncomfortable. The surgeon cannot correct this slight lateral positioning defect without repositioning the epiphysial part of the bone plate, which requires redrilling near the first holes so as to be offset. In practice, this is not possible since the holes are too close to each other, plus the surgical procedure is made longer and more complex, and more damage is done to the epiphysis.
It has therefore been suggested in US 2006/0089648 of Masini and U.S. Pat. No. 7,090,676 of Huebner to separate outer and inner parts of such a bone plate and pivot them together so their relative angular positions can be adjusted. These systems offer some improvement, but have the considerable disadvantage that they frequently fail in use, with the two parts, even if screwed tightly to each other during surgery, loosening and allowing the fracture to work, thereby impeding healing. The problem is that the bone plate is subjected to considerable mechanical action during and after surgery, but is of course totally inaccessible once the surgical field is closed. Thus the procedure of, for example, applying a cast might be enough to loosen it and basically make it useless.